Implementing ISA Server
Caching
Caching Overview
• ISA Server supports caching as a way to
improve the speed of retrieving information from
the Internet.
• From the internal user’s point of view, caching
improves Internet access performance.
• From the network administrator’s point of view,
caching provides the added benefit of reducing
the use of network bandwidth
• ISA Server extends the benefits of caching by
enabling scheduled content download jobs in
which ISA Server downloads Internet content to
the cache before any user requests the object
What Is Caching
• Caching stores Web content on the ISA Server
computer in memory or on the server’s hard
disk.
• When a user requests Web information that is in
the cache, ISA Server provides the information
from the cache, enabling a quicker response to
the client.
• ISA Server can be configured to enable the
caching of Hypertext Transfer Protocol (HTTP)
and File Transfer Protocol (FTP) objects.
benefits
• Improved performance
• Reduced bandwidth usage
How Caching Works
1. The Web proxy client sends a request for
content located on an Internet Web server. The
Web request is intercepted by ISA Server and
forwarded to the Web proxy filter.
• 2. ISA Server checks whether the requested
content is contained in its cache. If the content
is not in the cache, or if the content has
expired (that is, the header information in the
content indicates that it should no longer be
served from a cache),ISA Server forwards the
request to the Web server on the Internet.
3. The Web server on the Internet returns the information
requested.
4. The ISA Server Web proxy filter places the Web content
in its in-memory cache. ISA Server uses an in-memory
cache to store the most frequently requested content.
5. After placing the Web content in the in-memory cache,
ISA Server Web caching server returns the content to the
requesting user
6. After a time, the ISA Server Web proxy filter will copy the
contents of the in-memory cache to the disk-based
cache. If the content is not frequently accessed, the inmemory cache will flush the content and the only copy of
the content on ISA server will reside in the disk-based
cache.
Caching Scenarios
• ISA Server supports both forward and reverse
caching
• Forward caching occurs when a user on the
corporate network makes a request for Web
content located on an Internet Web server.
• The user initiates an HTTP, Hypertext Transfer
Protocol Secure (HTTPS), or FTP request to an
Internet Web server and the request is
intercepted by ISA Server. ISA Server retrieves
the content from the Internet Web server, stores
that content in its cache, and returns the content
to the user.
• Reverse caching occurs when users on the Internet
request Web content located on a server on the
corporate network that is accessible through a Web
publishing rule.
• When an Internet user requests content from the internal
server, ISA Server forwards the request to the Web
server. The Web server sends the requested content to
ISA Server, which then returns the content to the Internet
user who made the request.
• In this scenario, ISA Server will cache a copy of the
requested information so that the next request for the
same information can be provided from the ISA Server
cache rather than again accessing the internal Web
server
What Are Content Download Jobs?
• ISA Server extends caching performance by
enabling content download jobs.
• By monitoring and analyzing Internet access,
you can determine which Web content is most
likely to be requested by internal clients.
• You can then create a content download job to
download the Web content to the ISA Server
cache before any client requests the object.
• Content download jobs allow you to schedule
content for download at a specific time or at
recurring times.
Benefits of Using Content
Download Jobs
• The main reasons for using content
download jobs are to improve Internet
access performance and decrease the use
of bandwidth to the Internet.
How Content Download Jobs Work
1. Create a content download job that specifies
Web content to be retrieved from the Internet
and when content retrieval occurs.
2. At the scheduled time, ISA Server uses a
background process to retrieve the content from
the Web server. The content is stored in the ISA
Server cache based on the settings specified by
the content download job.
3. A user on the internal network sends a request
for the Web content to the ISA Server computer.
The Firewall service passes the request to the
Web proxy filter.
4. The ISA Server Web proxy filter determines that
the content is in the Web cache, so ISA Server
retrieves the content from the cache.
5. Content retrieved from cache is returned to the
requesting user
How Caching Is Implemented in
ISA Server
• RAM and disk caching:ISA Server
allocates RAM for caching popular objects
and caches other objects on disk.
• When caching an object, ISA Server first
places an object into the RAM cache and
then writes objects to disk.
• By default, ISA Server uses 10 percent of
the RAM on the server to cache Web
content
• Maintaining the RAM cache in physical
memory:
• Directory of cached object
• Single cache file
• Quick recovery
• Efficient cache updates
• Automatic cleanup
What Is Web Chaining and Caching
• Some organizations include multiple locations with
computers running ISA Server deployed in each location.
• In this scenario, you can combine caching with Web
proxy chaining to optimize caching performance.
• Web proxy chaining is useful when your organization has
multiple branch-office locations but all Internet requests
are routed through one location at the head office.
• Implement :install ISA Server in each office and then
configure ISA Server at the branch offices to route all
Internet requests to the ISA Server computer at the head
office.
benefits of using Web chaining
• If all the servers running ISA Server in the
branch offices are configured to forward
their requests to the head-office ISA
Server, the head-office ISA Server will
develop a large cache that contains many
requested items
branch-office/main-office scenario
branch-office/main-office scenario
1. The client sends a request for Web content to
the Web caching server at the branch office. If
the Web caching server at the branch office
contains a valid version of the Web content in
its cache, it will return the content to the
requesting user.
2. If the content requested by the branch-office
user is not contained in the branchoffice
server’s cache, the request is forwarded to an
upstream Web caching server in the Web
proxy chain.
3. If the upstream Web caching server has a valid copy of
the requested content in cache, the content is returned
to the branch-office Web caching server. The branchoffice Web caching server places the content in its own
Web cache and then returns the content to the branchoffice user who requested the content.
4. If the upstream Web caching server at the main office
does not contain the requested content in its cache, it
will forward the request to the Web server on the
Internet. The Internet Web server returns the requested
content to the main-office Web caching server. The Web
caching server at the main office places the content in
cache.
5. The main office returns the content to the
branch-office Web caching server. The
branch-office Web caching server places
the content in its cache.
6. The branch-office Web caching server
returns the content from its cache to the
requesting user.
Configuring Caching
• How to Enable Caching and Configure
Cache Drives
How to Configure Cache Settings
What Are Cache Rules
• Why Use Cache Rules
• EX: users in your organization may frequently
access a Web site, so you may want to
configure the cache so that all content from that
Web site is cached on the computer running ISA
Server.
• If the Web site contains critical information that
changes frequently, you may need to implement
the opposite solution, that is, configure the Web
site to never be cached.
Managing Cache Rules
• Modifying settings
• Managing rule order
• Disabling or deleting cache rules
• Export and import cache rules
Configuring Content Download
Jobs
• How to Configure Content Download Jobs